tcp-echo.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"net"
	"strings"
	"sync"
)

func handleReq(conn net.Conn) error {
	reader := bufio.NewReader(conn)

	for {
		message, err := reader.ReadString('\n')

		if err != nil {
			return err
		}

		fmt.Print("Message Received:", string(message))
		conn.Write([]byte(strings.ToUpper(message) + "\n"))
	}
}

func main() {

	fmt.Println("Launching server...")

	ln, _ := net.Listen("tcp", ":8081")

	defer ln.Close()

	count := 0
	conns := make(chan net.Conn)
	errs := make(chan error)

	go func() {
		for {
			conn, _ := ln.Accept()

			conns <- conn
		}
	}()

	mutex := &sync.Mutex{}

	for {
		select {
		case conn := <-conns:
			mutex.Lock()
			count += 1
			mutex.Unlock()

			println("active clients: ", count)

			go func(conn net.Conn) {
				err := handleReq(conn)

				if err != nil {
					conn.Close()
					errs <- err
				}
			}(conn)
		case err := <-errs:
			if err == io.EOF {
				mutex.Lock()
				count -= 1
				mutex.Unlock()

				println("active clients: ", count)
			} else {
				println(err.Error())
			}

			break
		}
	}
}